The invention relates to a magnet coil arrangement having an encapsulated coil, which comprises a coil former that is provided with a winding and is extrusion coated with plastic, and having a metal housing which is pushed over the encapsulated coil and surrounds it, as claimed in the precharacterizing clause of claim 1.
A magnet coil arrangement of this type is known from DE 198 54 100 A1. A coil former which is provided with a winding is extrusion coated with plastic and forms an encapsulated coil. A plug cap is integrally formed on the encapsulated coil. Contact lugs are held in the plug cap, two of which are connected to the ends of the winding, while a third is associated with the protective ground conductor connection. The electrical connection is made via a connecting plug which is plugged onto the contact lugs. The housing of the connecting plug provides an external seal for the contact area which is formed by it and the plug cap. A metal housing is pushed over the encapsulated coil. In the process, the metal housing engages in a recess between the plug cap and the outer surface of the encapsulated coil. The plug cap is provided with a recess, through which a connecting element is passed. The connecting element produces the electrical contact between the metal housing and the contact lug that is associated with the protective ground conductor connection. A sealing element is arranged between the connecting element and the recess in the plug cap and rests both on the circumferential surface of the connecting element and on the inner surface of the recess in the plug cap, forming a seal. The sealing element prevents moisture which has penetrated in between the outer surface of the encapsulated coil and the metal housing from being able to reach the connection area. In one exemplary embodiment, the connecting element is in the form of a screw, which is passed through a hole in the contact lug that is associated with the protective ground conductor connection, and whose thread is screwed into the metal housing. In this case, the contact lug is clamped in between the head of the screw and the plug cap. Even if the screw is tightened during assembly with a torque which is sufficient to make electrical contact, it is impossible to preclude the possibility of the plastic of the plug cap changing its characteristics over the course of time, in particular shrinking or changing its elasticity. This can lead to the contact resistance between the contact lug and the screw head becoming greater, such that an adequate electrical contact is no longer provided. There is no such risk when the connecting element—as in another exemplary embodiment in DE 198 54 100 A1—is connected to the contact lug and the metal housing via a metallic push connection in each case. In this situation, any change in the characteristics of the plastic that is used for the plug cap has no disadvantageous influence on the electrical contact resistance between the contact lug and the connecting element, or between this and the metal housing.
The invention is based on the object of ensuring a permanent electrical contact between the contact lug and the metal housing in a magnet coil arrangement of the type mentioned initially, even when the contact lug that is associated with the protective ground conductor connection is connected to the metal housing by means of a screw connection.
This object is achieved according to the invention by the features wherein a component is connected by a force fit to the tubular metal part which is arranged between the contact lug and the metal housing, and this component ensures that a reliable electrical contact is made in the long term, irrespective of the material characteristics of the plastic that is used for the plug cap.
Advantageous developments of the invention concern the design of configuration of the connecting element between the contact lug and the metal housing, including the electrically conductive connection between the contact lug, the connecting element and the metal housing, as well as to the configuration of the sealing elements which are arranged between the connecting element and the cutout in the plug cap.